Valley Water has been undertaking pilot studies to evaluate the feasibility of different types of NBS to identify the most efficient and cost-effective option (or combination of options). These pilot projects include:
- Open-Water Treatment Cells
- Horizontal Levees
- Floating Wetlands
Open Water Treatment Cells
Open water treatment cells use natural processes, such as sunlight and the activity of bacteria and algae, to break down contaminants. These shallow cells allow sunlight to penetrate, helping to reduce pollutants such as nitrates and some organic compounds.
A pilot study at SVAWPC from 2017–2019 integrated ozonation before the cells to improve efficiency. Results showed the cells removed 28% to 47% of nitrates, especially in summer when sunlight is more intense, and reduced some pharmaceuticals and organic compounds. However, metals like copper and nickel were harder to treat, and pesticide removal was limited. Potential improvements could include extending the residence time of ROC in the cells or enhancing pre-treatment with advanced oxidation processes like ozonation. While open water treatment cells present a sustainable solution with potential co-benefits, their efficiency can vary with seasonal changes, and they require substantial land areas for implementation.
Floating Wetlands
Floating wetlands are an engineered natural treatment system where water flows through the roots of hyperaccumulating plant species growing on floating platforms. These roots support provide high surface area for biofilms that adsorb and extract contaminants. These biofilms enhance nutrient uptake and facilitate the breakdown of contaminants through natural processes.
Valley Water has been testing floating wetlands at SVAWPC, showing promising results in reducing nitrogen and copper, especially in warmer months when biological activity increases. However, they were less effective at removing contaminants like nickel and phosphorus and faced challenges with high salinity levels in the ROC. Further improvements in design and plant selection could enhance their performance. When land is available, floating wetlands provide an eco-friendly way to treat ROC while offering added benefits to the community.
Horizontal Levees
Horizontal levees are subsurface flow wetlands designed to provide flood protection, habitat restoration, and water treatment. These levees are constructed with a gradual slope filled with layers of gravel, sand, and woodchips, which filter the water as it flows through, leveraging microbial processes to break down contaminants.
In 2020, Valley Water joined the horizontal levee pilot project at Oro Loma Sanitary District (OLSD) in partnership with UC Berkeley, East Bay Dischargers Authority, and San Francisco Estuary Institute. ROC from the SVAWPC was transported to OLSD at a rate of 10,000 gallons/week and then fed to horizontal levee cells to evaluate the removal of nutrients and metals.
Phase 1 of this project was completed in 2022 and yielded encouraging results indicating that cells receiving ROC exhibit removal of nutrients, trace organic contaminants, copper, and showed improvement of general water quality parameters. However, the removal efficiency for certain trace organic contaminants was lower, likely due to differences in redox conditions.
To enhance overall performance, adjustments such as optimizing the slope, substrate composition, and redox conditions have been considered for Phase 2, of this project particularly for improving the removal of persistent metals and organic pollutants.
Phase 2, launched in 2022, aims to improve treatment efficiency by enhancing cell design and addressing emerging contaminants like PFAS using advanced materials like geo-media and activated carbon. Beyond water treatment, horizontal levees help protect against storm surges and sea-level rise, supporting Valley Water’s commitment to sustainable, eco-friendly infrastructure.